1. Field of the Invention
The present invention relates to a process for isomerizing allenes to alkynes.
2. Description of the Related Arts
As for a conventional process for isomerizing an acetylene-type compound to an allene-type compoun, there has been a disclosure, for example, Japanese Unexamined Patent Publication (KOKAI) No. 47-38,593, on a conventional isomerization process which is processed by using metallic ruthenium as a catalyst at room temperature in order to alternately isomerize the acetylene-type compound and the allene-type compound. Moreover, there has been another disclosure, for example, Japanese Unexamined Patent Publication (KOKAI) No. 4-225,987, on another conventional isoinerization process in which an allene-type hydrocarbon compound is isomerized to produce metallized 1-alkyne by using a mixture of alkylamine and alkali metal hydride as an isomerization catalyst in the presence of alkali metal.
It has been revealed recently that mixtures of allenes, such as CH.sub.2 .dbd.C.dbd.CH.sub.2, and alkynes, such as HC.ident.C--CH.sub.3, give copolymers (or reactive elastomers) by organometallic catalysts represented by Ni complexes. In the laboratory level synthesis, it is possible to obtain both allene and propyne in their pure forms, and to control the compositional ratios of the resultant copolymers by mixing them in arbitrary ratios. However, it is quite difficult to separate them in a large scale because their physical properties, such as a boiling point, are very close (see allene (bp. -32.degree. C.), propyne (bp. -23.degree. C.).).
The MAPP gas has been known, and is commercially available as a material supply source of allene/propyne. The MAPP gas contains allene in an amount of from 18 to 28% by weight, propyne in an amount of from 23 to 36% by weight, and propylene and butane in an amount of from 1 to 8% by weight. However, it is difficult to adjust the composition of the MAPP gas at a desired compositional ratio. Therefore, the conventional technique, in which the metallic ruthenium is used as a catalyst, is not proper industrially, because the isomerization reaction is carried out by utilizing the thermodynamic equilibrium. Accordingly, the isomerization reaction develops slow. Further, the publication does not set forth on how to control the isomerization reaction. Consequently, there arises a drawback in that the composition ratio cannot be selected. Furthermore, there is another problem in that the expensive metallic ruthenium is used as a catalyst.
When the allenes and alkynes are used as monomers for polymerization, it is essential to employ a step of drying the monomers. This is because the organometallic compounds, which are prepared from transition metals, are used as a catalyst. However, it is impossible to isomerize and dry the allenes and alkynes at the same time.
In the latter process, drying is not effective during the isomerization reaction. Moreover, when carrying out the allene/alkyne polymerization by using the resulting isomerized product, there arises a drawback in that the alkylamine contained in the isomerization catalyst poisons the polymerization catalysts.
It is an assignment to be solved by the present invention and given thereto to provide a process which can isomerize allenes to alkynes less expensively and stably.